Reduced food availability induces behavioural changes in Griffon Vulture Gyps fulvus

Abstract

In natural conditions, Griffon Vultures typically show shy behaviour and escape by flying if approached by humans. According to the state-dependent foraging theory, Griffon Vultures should modify their foraging behaviour depending on food availability and predation risk, humans being the main potential predator. We tested the Reaction Time (RT) and Flight Initiation Distance (FID) in five different artificial feeding schemes over three years in which food availability in the field varied significantly. The first scenario was set in a so-called “vulture restaurant”, in which government employees feed vultures that may exhibit tame behaviour and stay within a few meters from a feeding person. Scenario 2 involved similar conditions, but here the researchers not employees placed the food in the vulture restaurant. The vultures did not land at the restaurant until one day had passed, and they flew away when people approached them within 250 m. The third scenario was established in a local zoo several months after the closure of the vulture restaurant. Here, employees fed captive vultures that were often accompanied by wild birds that landed to take food. The RT was 14.2 min and the FID was 50 m. The fourth scenario was established during the subsequent breeding season in a mountain where vultures were fed by the authors of the present study. The RT was 2.8 min and the FID was 15.2 m. The fifth scenario was established in another mountain after the breeding season. Now, the RT was 19.2 min and the FID was 52.2 m. These results demonstrate the ability of vultures to evaluate the predation risk depending on food availability and their state of hunger, and their ability to modify their behaviour from “natural” caution (”shyness”) towards a more tolerant (”fearless”) behaviour.